This invention relates in general to electromagnetic coil assemblies and in particular to an interlocking bobbin and cap structure for use in such an electromagnetic coil assembly.
Electromagnetic coil assemblies are well known devices which are employed in a wide variety of applications. One basic structure for an electromagnetic coil assembly includes a bobbin formed of an electrically non-conductive material. The bobbin includes a generally cylindrical body (usually hollow) having enlarged end flanges provided at both ends thereof. An annular cavity is defined about the outer surface of the cylindrical body between the two end flanges, within which a length of an electrical conductor, such as a metallic wire, is wound. The two ends of the wound coil of the electrical conductor (commonly referred to as the magnet wire) are connected through respective lead wires to an external source of electrical current. When energized, the electrical current passing through the coil generates an electromagnetic field. This electromagnetic field can be used for many purposes, such as to cause movement of a movable component formed from a magnetically permeable material located near the coil.
To facilitate the connection of the two ends of the magnet wire to the respective lead wires, a pair of slots are usually formed through one of the end flanges of the bobbin. The first slot extends from the outer peripheral edge of the end flange radially inwardly to the outer surface of the cylindrical body of the bobbin. The start winding of the coil of magnet wire is threaded from the exterior surface of the end flange through this first slot to the cylindrical body of the bobbin to begin the winding process. The second slot extends from the outer peripheral edge of the end flange radially inwardly only partially toward the outer surface of the cylindrical body of the bobbin. The finish winding of the coil of magnet wire is threaded from the outer surface of the wound coil through this second slot to the exterior surface of the end flange of the bobbin. The two ends of the magnet wire are connected to the respective lead wires located on the exterior surface of the end flange of the bobbin.
In electromagnetic coil assemblies of this general type, it is important to provide secure connections between the two ends of the magnet wire and the respective lead wires. To accomplish this, the exterior surface of the end flange of the bobbin may be formed having labyrinth structure, through which the two lead wires are threaded. This labyrinth structure functions to frictionally retain the lead wires on the end flange of the bobbin, thereby preventing them from being accidentally withdrawn and becoming separated from the ends of the magnet wire. Also, adhesive tape may also be used to retain the two ends of the magnet wire and the respective lead wires together, preventing them from being disconnected from one another. Preferably, the adhesive tape is also formed from an electrically non-conductive material so as to electrically insulate the two connections and prevent a short circuit from occurring.
The feeding of the lead wires through the labyrinth structure and the application of the adhesive tape are operations which are typically performed by hand during manufacture of the electromagnetic coil assembly, especially when the physical size of the electromagnetic coil assembly is relatively small. Also, to insure that the connections between the two ends of the magnet wire and the respective lead wires are sufficiently insulated and that the lead wires will not be accidentally pulled out, a relatively large amount of the adhesive tape is also generally applied to the connections. As a result, the manufacture of electromagnetic coil assemblies of this general type is relatively slow and expensive. Thus, it would be desirable to provide an improved structure for an electromagnetic coil assembly which prevents the accidental withdrawal of the lead wires and which electrically insulates the connections between the two ends of the magnet wire and the respective lead wires, yet which is also relatively simple and inexpensive to construct and assemble.